Northern England once had a distinct civilisation, a way of living different to the south, and though most of it has vanished now with the cotton, coal and wool, occasional rituals unexpectedly survive. Pigeon lofts in County Durham, giant leeks in Northumbria - but the harvesting of forced rhubarb is perhaps the most surprising example because it's not an amusement, but a small industry.

The season begins in January. Last week, in a few old sheds near Wakefield, groups of men moved carefully among the pink rows, tenderly plucking the rhubarb stems. A hushed atmosphere; the farmer, Janet Oldroyd-Hume, said that if you stood quietly you could hear the rhubarb grow: the gentle pop of a bulb, the creaking of a stem. Most of the shed was pitch-dark, save at the picking end where the men stooped by candle-light, each candle on an iron pole with the other end spiked like a shooting stick. Joseph Wright of Derby would have caught the chiaroscuro nicely. As it was, I thought that if that previous northern civilisation needed some kind of sacred embodiment - some ceremony that preserved the memories of sarsaparilla, Fleetwood hake, Methodist chapels, factory whistles, wakes weeks and Whitsun walking days - then these shadows picking rhubarb by candlelight would be it, the shed its low cathedral.

Oldroyd-Hume grows about 1,000 tonnes of rhubarb every year, most of it harvested in summer outside in the fields, but about 200 tonnes of it is forced as a winter crop in the sheds. The Oldroyd family have been farmers for several generations, but it was her father, Ken, Yorkshire's "rhubarb king", who began the family's specialism and won medals for it. When the king was a child, his grandfather had taken him through the "secret door" that led to the sheds; a privilege because children could easily damage the crop and were forbidden. "He knew then that that's what he wanted to do for the rest of his life," his daughter said.

This was just before the second world war when West Yorkshire was at the peak of its rhubarb production, with about 200 growers, who sent their crop by train to London markets. Today, according to Oldroyd-Hume, there are only a dozen. But the worst times are over. For the past 20-odd years, rhubarb has slowly been reclaiming its place at the British table, in chutneys and sauces as often as crumbles, thanks to a new generation of chefs and "new British cooking" that have transformed rhubarb from a provincial pudding into a metropolitan delicacy.

Sugar is integral to rhubarb's story, changing its role in the human diet during the 18th century from a medicinal vegetable to a false fruit. It was the bitter memory of wartime crumbles lacking sugar, according to Oldroyd-Hume, that made postwar Britain screw up its face against rhubarb and turn instead to the imported peaches, bananas and grapes that were heaped high in the shops whatever the season. Rhubarb became historic, and comic. It was a laxative, it was the word actors used in murmuring crowds, its leaves (slightly poisonous) reminded us of allotments seen from trains, or Dad's back garden and the hole where the air raid shelter had been. And yet in the 19th century, so much effort had gone into making fresh rhubarb available all year as a supplement to the apples and pears that lay stored on shelves, getting softer by spring. The solution was to make rhubarb grow unnaturally - forcing.

The legend is that in 1817 or thereabouts workmen digging a trench in Chelsea accidentally covered some rhubarb roots with soil. Then, on removing the soil, they found the roots had grown long, tender-looking pink sticks. "Luckily, it was Chelsea," Oldroyd-Hume said ambiguously, "so they tasted them."

By 1877 a technique was perfected that in its principles has stayed much the same. Roots are planted outside in the fields and given a top-dressing of "shoddy", the waste that comes when fleeces are combed and carded in woollen mills (Yorkshire still has one or two, though little of their wool comes from Pennine sheep: botanists have identified new weeds in the Oldroyd fields that come from the Falkland Islands, Australia and New Zealand). Later, in the sheds, the stems shoot up, struggling to find the light. If it happened to animals, we would be squeamish.

There have been some changes in cultivation. Yorkshire coal no longer warms the air, the pickers come from eastern Europe, and tourists come to see the sheds. Lack of early frosts, important to rhubarb, has meant a season starting in January rather than December.

Rhubarb owes its revival, Oldroyd-Hume said, to a growing taste for tartness, and also to an appreciation of its high potassium and calcium content, which may help reduce cholesterol and prevent deep vein thrombosis.

Well and good. But there is also the role of rhubarb as the madeleine (Proust refuses to be kept out of food) to a postwar generation that was sometimes given a raw stick to dip in the sugar. In fact, many of us have two kinds of madeleine: liquorice is the other. Neither plant was native to Britain - liquorice grew first in the Middle East - but both were grown in the same acreage of Yorkshire. Odd that this small space should have furnished so many childhood diets, I thought, and took a taxi from Oldroyd's to the outskirts of Pontefract where I met Tom Dixon, a member of the Pontefract Liquorice Trust. In his kitchen he produced a large bag of show-and-tell: a big lump of liquorice looking as mineral as coal; a sheet of liquorice to demonstrate how Chaplin's edible boots had been made for The Gold Rush (Chaplin ate the laces like spaghetti); a photo of John Betjeman (author of The Licorice Fields at Pontefract) standing in a field behind this very house.

Two Pontefract factories still turn out sweets from the exports of Turkey, Iraq and Iran, but the last of Yorkshire's root crop was dug 40 years ago. Instead, there is Pontefract's new annual liquorice fair: liquorice-growing as folklore. And as liquorice is 50 times sweeter than sugar, and therefore hundreds of times sweeter than rhubarb, nobody in these times can hope for a revival.